Ultrasonic image generating device and image generating method

ABSTRACT

An ultrasonic image generating device which generates a cross-sectional image of a specific cross-section of a subject from ultrasonic images obtained by scanning the subject from a plurality of directions using an ultrasonic probe, includes: a cross-section position identifying unit which obtains cross-section information indicating a position and an orientation of the specific cross-section; a positional information obtaining unit which obtains positional information including a position and an orientation of each of the ultrasonic images of the subject; a reference image selecting unit which selects at least one of the ultrasonic images as a reference image, the at least one of the ultrasonic images having a distance from the specific cross-section that is less than a first threshold and an orientation difference from the specific cross-section that is less than a second threshold; and a cross-sectional image generating unit which generates the cross-sectional image using the reference image.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation application of PCT Patent Application NoPCT/JP2011/006960 filed on Dec. 13, 2011, designating the United Statesof America, which is based on and claims priority of Japanese PatentApplication No. 2010-287291 filed on Dec. 24, 2010. The entiredisclosures of the above-identified applications, including thespecifications, drawings and claims are incorporated herein by referencein their entirety.

FIELD

One or more exemplary embodiments disclosed herein relate generally toultrasonic image generating devices and image generating methods, and inparticular, to an ultrasonic image generating device which generatescross-sectional images of specific cross-sections of a subject fromultrasonic images obtained by scanning the subject from a plurality ofdirections using an ultrasonic probe.

BACKGROUND

An X-ray diagnostic device, a magnetic resonance (MR) diagnostic device,and an ultrasonic diagnostic device are widely used as diagnosticimaging devices for examining bodies. In particular, the ultrasonicdiagnostic device has advantages such as its non-invasive nature andreal-time performance and is widely used for diagnostics includingmedical examinations. The ultrasonic diagnostic device is used indiagnostics for a variety of regions of the body including heart, liver,and a breast. One of the most important regions is the breast due tohigh morbidity and increased number of patients of breast cancers.

Hereinafter, a description is given of an example where a breast isexamined. For ultrasonically examining a breast, imaging is performedwhile scanning an ultrasonic probe over the breast. Here, due to contactstate between the ultrasonic probe and the breast or deformity of thebreast, image degradation of the ultrasonic images or deformation ofmammary tissue occurs. Therefore, ultrasonic images taken from onedirection may not be sufficient for an accurate diagnosis.

In view of this, a method has been recently gaining attention where athree-dimensional tissue structure within the breast is constructed fromtemporally-different ultrasonic images obtained by scanning using aultrasonic probe. The method increases diagnostic accuracy by observingthe same region from different directions. For constructing thethree-dimensional tissue structure, each ultrasonic image is mapped intothe three-dimensional space based on the positional information of theultrasonic image (position and orientation of the ultrasonic probe). Thepositional information is obtained from, for example, a camera, varioustypes of sensors such as a magnetic sensor and an acceleration sensor,or a robotic arm.

CITATION LIST Patent Literature

[PTL 1]

-   Japanese Patent No. 3619425

SUMMARY Technical Problem

However, there is a need for an ultrasonic image generating device withhigher accuracy.

One non-limiting and exemplary embodiment provides an ultrasonic imagegenerating device with an increased accuracy.

Solution to Problem

In one general aspect, the techniques disclosed here feature anultrasonic image generating device which generates a cross-sectionalimage of a specific cross-section of a subject from a plurality ofultrasonic images obtained by scanning the subject from a plurality ofdirections using an ultrasonic probe, and includes: a cross-sectionposition identifying unit which obtains cross-section informationindicating a position and an orientation of the specific cross-section;a positional information obtaining unit which obtains positionalinformation including a position and an orientation of each of theultrasonic images of the subject; a reference image selecting unit whichselects at least one of the ultrasonic images as a reference image, theat least one of the ultrasonic images having a distance from thespecific cross-section that is less than a first threshold and anorientation difference from the specific cross-section that is less thana second threshold; and a cross-sectional image generating unit whichgenerates the cross-sectional image using the reference image.

Additional benefits and advantages of the disclosed embodiments will beapparent from the Specification and Drawings. The benefits and/oradvantages may be individually obtained by the various embodiments andfeatures of the Specification and Drawings, which need not all beprovided in order to obtain one or more of such benefits and/oradvantages.

Advantageous Effects

One or more exemplary embodiments or features disclosed herein providean ultrasonic image generating device with an increased accuracy.

BRIEF DESCRIPTION OF DRAWINGS

These and other advantages and features will become apparent from thefollowing description thereof taken in conjunction with the accompanyingDrawings, by way of non-limiting examples of embodiments disclosedherein.

FIG. 1 is a block diagram of an ultrasonic image generating deviceaccording to Embodiment 1.

FIG. 2A illustrates a use example of the ultrasonic image generatingdevice according to Embodiment 1.

FIG. 2B is a diagram illustrating a volume image obtained by theultrasonic image generating device according to Embodiment 1.

FIG. 2C illustrates a cross-sectional image obtained by the ultrasonicimage generating device according to Embodiment 1.

FIG. 3 is a block diagram illustrating a configuration of the ultrasonicimage generating device according to Embodiment 1.

FIG. 4 is a block diagram illustrating a configuration of an imageprocessing unit according to Embodiment 1.

FIG. 5 is a flowchart of processing for generating an image of aspecific cross-section according to Embodiment 1.

FIG. 6 is a flowchart of processing for selecting reference imagesaccording to Embodiment 1.

FIG. 7 is a flowchart of processing for generating pixel values of thespecific cross-section according to Embodiment 1.

FIG. 8 is a flowchart of a variation of processing for generating pixelvalues of the specific cross-section according to Embodiment 1.

FIG. 9A is a diagram illustrating a group of ultrasonic images obtainedwhen scanning is performed using a ultrasonic probe in the y-axisdirection according to Embodiment 1.

FIG. 9B is a diagram illustrating a group of ultrasonic images obtainedwhen scanning is performed using the ultrasonic probe in the x-axisdirection according to Embodiment 1.

FIG. 9C is a diagram illustrating reference images and a cross-sectionalimage according to Embodiment 1.

FIG. 10 is a diagram illustrating an example where reference images areselected, according to Embodiment 1.

FIG. 11 is a diagram illustrating another example of a volume imageobtained by the ultrasonic image generating device according toEmbodiment 1.

FIG. 12 is a flowchart of a variation of the processing for selectingreference images according to Embodiment 1.

FIG. 13 is a block diagram of a variation of the ultrasonic imagegenerating device according to Embodiment 1.

FIG. 14 is a diagram illustrating sensitivity of a Doppler imageaccording to Embodiment 1.

FIG. 15A is a diagram illustrating a flexible disk according toEmbodiment 2.

FIG. 15B is a diagram illustrating a structure of the flexible diskaccording to Embodiment 2,

FIG. 15C is a diagram illustrating a computer system according toEmbodiment 2.

FIG. 16 is a block diagram illustrating a configuration of an ultrasonicimage generating device according to a reference example.

FIG. 17 is a block diagram illustrating a configuration of an imageprocessing unit according to a reference example.

FIG. 18A is a diagram illustrating an example of scanning using theultrasonic probe.

FIG. 18B is a diagram illustrating resolution of the x-z plane whenscanning is performed using the ultrasonic probe in the y-axisdirection.

FIG. 18C is a diagram illustrating resolution of the y-z plane whenscanning is performed using the ultrasonic probe in the y-axisdirection.

FIG. 18D is a diagram illustrating a cubic shape that is a targetobject.

FIG. 18E is a diagram illustrating a volume image.

FIG. 18F is a diagram illustrating resolution in a three-dimensionalspace.

FIG. 18G is a diagram illustrating resolution in the y-z plane.

FIG. 18H is a diagram illustrating resolution in the x-y plane,

FIG. 19A is a diagram illustrating target objects to which ultrasonicwaves are emitted.

FIG. 19B is a diagram illustrating a volume image obtained when scanningis performed using the ultrasonic probe in the y-axis direction.

FIG. 19C is a diagram illustrating volume images obtained when scanningis performed using the ultrasonic probe in the x-axis direction.

FIG. 19D is a diagram illustrating a volume image obtained by thecombining.

FIG. 19E is a diagram illustrating a cross-sectional mage cut out fromthe volume image.

FIG. 19F is a diagram illustrating a correct cross-sectional image,

DESCRIPTION OF EMBODIMENT(S) (Underlying Knowledge Forming Basis of thePresent Disclosure)

Referring to FIG. 16 and FIG. 17, the following describes an ultrasonicdiagnostic device, according to a reference example, which reconstructsa three-dimensional tissue structure based on the positional informationat the time of ultrasonic image obtainment and which synthesizesarbitrary cross-sectional images from the three-dimensional tissuestructure.

FIG. 16 is a block diagram illustrating an overall configuration of anultrasonic image generating device 500 according to a reference example(an ultrasonic diagnostic device). Elements such as piezoelectricelements arranged in an ultrasonic probe 101 generate ultrasonic signalsbased on driving signals provided from a transmitting unit 102. Theultrasonic signals are reflected from the structure in a body such asmammary gland and muscle. Part of the reflected components return to theultrasonic probe 101 and is received by the ultrasonic probe 101. Areceiving unit 103 generates reception radio frequency (RF) signals byperforming, on the reflected signals received, amplification andanalog-to-digital (A/D) conversion, and by, for example, performingdelay add processing on the signals of the respective elements.

Here, the operations of the transmitting unit 102 and the receiving unit103 are controlled by a transmission and reception control unit 104.More specifically, for the transmitting unit 102, the transmission andreception control unit 104 switches between driving voltages, set atransmission frequency and so on for certain scanning. The transmissionand reception control unit 104 sets the receiving unit 103 delay timeand so on for performing reception beam forming. The reception RFsignals are provided to a B-mode processing unit 105, a Dopplerprocessing unit 106 and a strain processing unit 107.

The B-mode processing unit 105 performs, for example, logarithmicamplification and envelope demodulation on the reception RF signals togenerate B-mode data (also referred to as a B-mode image) in which thesignal intensity is expressed as a brightness level. The B-modeprocessing unit 105 provides the B-mode data to an image memory 108.

The Doppler processing unit 106 analyzes the frequency domain of thereception RF signals, and calculates, for example, flow rate or movementvelocity of tissue based on the Doppler effect caused by blood flow ortissue movement. The Doppler processing unit 106 then provides thecalculation result to the image memory 108 as Doppler data.

The strain processing unit 107, for example, calculates the amount ofstrain of the tissue between two different points, using the movement ofa specific portion obtained from the reception RF signals. The strainprocessing unit 107 then provides the calculation result to the imagememory 108 as strain data.

An image processing unit 509 selects data to be displayed from amongvarious types of data stored in the image memory 108, and appliespredetermined image processing on the selected data. A display unit 112displays the processing result.

A positional information obtaining unit 110 and a cross-sectionalposition identifying unit 111 provide, to the image processing unit 509,positional information of the cross-section necessary for obtainingdesired cross-section in the three-dimensional space.

More specifically, the positional information obtaining unit 110 obtainspositional information 203 of the ultrasonic probe 101 at the time ofultrasonic image obtainment, based on output signals from a camera, amagnetic sensor, and so on The cross-sectional position identifying unit111 receives the cross-section information 202 indicating the positionalinformation of a cut-out cross-section (hereinafter, referred to asspecific cross-section) from a user, and provides the receivedinformation to the image processing unit 509.

The image processing unit 509 generates a volume image 206 (volume data)which is a three-dimensional image in which ultrasonic images are mappedinto the three-dimensional space. The image processing unit 509generates a cross-sectional image 605 of the specific cross-sectionidentified by the cross-section information 202, using the volume image206 mapped into the three-dimensional space based on the positionalinformation 203,

FIG. 17 is a block diagram illustrating a processing unit, included inthe image processing unit 509, used for generating the cross-sectionalimage of the specific cross-section. The image processing unit 509constructs the volume image by mapping the obtained ultrasonic imagesinto the three-dimensional space based on the positional information203. The three-dimensional space is constructed by fundamental unitseach referred to as a voxel which corresponds to a pixel intwo-dimensional space. For example, dividing a 10×10×10 cm cube into 1cm units allows the creation of voxels where each voxel has a volume of1×1×1 cm, and the entire cube is constructed by 10×10×10 voxel units.For mapping, pixel values of the ultrasonic images are assigned to thenearest voxels.

After the cross-sectional position identifying unit 111 identifies thespecific cross-section, the image processing unit 509 performsnearest-neighbor interpolation or bicubic interpolation based on thevalues of the voxels present near the coordinate positions of therespective pixels in the identified cross-section, to generate the pixelvalues of the pixels. The following describes the operations of eachprocessing unit.

A frame image input unit 191 obtains an index number 211 of atwo-dimensional image such as a B mode image or a Doppler image. Apositional information determining unit 192 determines, based on thepositional information 203 obtained from a sensor, positionalinformation 212 corresponding to the two-dimensional image having theindex number 211. The volume generating unit 199 then maps thetwo-dimensional image having the index number 211 into thethree-dimensional space based on the positional information 212. Themapping is performed on all of the target frames. The constructed volumeimage is stored in a volume memory 198. The voxel data at the positionwhere no frame image is present is interpolated using the value ofnearby voxel data. The volume image, which is mapped into thethree-dimensional space using frame images, is generated in such amanner.

A cross-sectional image generating unit 597 generates a cross-sectionalimage 605 by synthesizing the respective pixel values in thecross-section identified by the cross-section information 202 from thevalues of the voxels near the pixels, and provides the generatedcross-sectional image 605 to the display unit 112. The display data ofthe volume image 206 is provided from the volume memory 198 to thedisplay unit 112.

As described, the ultrasonic image generating device 500 according to areference example first constructs a volume image, and then synthesizesimages of arbitrary cross-sections using the voxel values within thevolume image.

For example, an ultrasonic diagnostic device according to PatentLiterature 1 writes echo data into memory addresses on a wavetransmission/reception coordinate system that is a coordinate calculatedfrom the position of the probe at the time of measurement, and storesthe voxel data in association with the wave transmission/receptioncoordinate system. Then, a transformation table is generated whichindicates the position of the cross-sectional image identified by theuser in the wave transmission/reception coordinate system (thecross-section identified in the wave transmission/reception space). Theultrasonic diagnostic device interpolates and generates echo data of thepixels on the cross-sectional image, using the voxel data located at theneighboring addresses.

The quality of the specific cross-sectional image generated by such anultrasonic image generating device depends on the quality of the volumeimage generated based on the voxel data. Thus, the volume image needs tohave high-resolution. In Patent Literature 1, however, no considerationhas been made as to a point that the frame images, used for generatingthe volume image, have different resolution depending on the scanningdirection of the ultrasonic probe,

A description is given of the direction dependency of the resolution,

FIG. 18A to FIG. 18H are diagrams for describing the directiondependency of the resolution. FIG. 18A is a diagram illustrating a statewhere the ultrasonic probe 101 is scanned in y-direction. FIG. 186 andFIG. 18C illustrate resolution of respective planes when the ultrasonicprobe 101 is scanned in the y-direction. FIG. 18B illustrates theresolution of the x-z plane which is perpendicular to the scanningdirection. FIG. 18C illustrates the resolution of the y-z plane which isparallel to the scanning direction.

As shown in FIG. 18C, the resolution decreases in the scanning direction(y-direction in FIG. 18C) in the plane parallel to the scanningdirection (hereinafter, referred to as C-plane). This is because theregion of propagation of ultrasonic waves in a medium expands relativeto the scanning direction. This phenomenon occurs when the ultrasonicprobe has at least one transducer. Such a phenomenon is particularlynoticeable in an ultrasonic probe including at least one row ofultrasonic transducers, because it is not possible to focus ultrasonicbeams by adding phase differences to ultrasonic waves emitted from thetransducers arranged in the scanning direction. It is assumed here thatthe array direction of the ultrasonic transducers is substantiallyperpendicular to the scanning direction of the ultrasonic probe.

The resolution of the plane (hereinafter, referred to as B—plane)perpendicular to the scanning direction of the ultrasonic probe andparallel to the array direction of the ultrasonic transducers is higherthan that of the C-plane. FIG. 18E illustrates a volume image generatedby reflected waves of the ultrasonic waves emitted to a cubic targetobject shown in FIG. 18D. Since the resolution of the y-axis directionis decreased, the resultant has a rectangle-shape which extends in they-axis direction as shown in FIG. 18E.

FIG. 18F, FIG. 18G, and FIG. 18H each illustrates direction dependencyof the ultrasonic images presented in the three-dimensional space. FIG.18F illustrates the resolution in the three-dimensional space. FIG. 18Gillustrates the resolution in the x-z plane. FIG. 18H illustrates theresolution in the x-y plane.

The square in the drawing is the minimum unit that can show up on theimage on the x-z plane. The rectangle in the drawing is the minimum unitthat can show up on the image on the y-z plane. Therefore, the minimumresolution of the ultrasonic probe in the scanning direction is lowerthan the minimum resolution in the direction perpendicular to thescanning direction.

A description is given of the phenomenon using another example.

FIG. 19A to FIG. 19F each illustrates a volume mage constructed based onthe ultrasonic images generated by scanning the target object fromdifferent directions. Referring to these drawings, a description isgiven of the problems caused when arbitrary cross-section images aresynthesized from the volume image.

FIG. 19A illustrates target objects to which ultrasonic waves areemitted. Along the y-axis, two cubes are arranged. FIG. 19B illustratesa resultant image generated by using reflected signals obtained byscanning the target objects along the y-axis direction using theultrasonic probe. FIG. 19C illustrates a resultant image generated byusing the reflected signals obtained by scanning the target objectsalong the x-axis direction using the ultrasonic probe.

For volume image construction, resultant of scanning from differentdirections are combined. In this example, the image shown in FIG. 19B iscombined with the image shown in FIG. 19C. FIG. 19D illustrates a volumeimage obtained by the combining. The volume image has a decreasedresolution because the images having decreased resolution in thescanning direction are combined. Thus, although the target objects areactually two separate objects, they cannot be shown separately in thevolume image.

When an arbitrary cross-sectional image is generated from the volumeimage, the cross-sectional image is cut out from the volume image shownin FIG. 19D.

FIG. 19E illustrates an image of the cross-section parallel to the y-zplane and cut out from the volume image in FIG. 19D. The image, ofcourse, does not show the two target objects separately, but shows onerectangle in which the two target objects are combined. FIG. 19Fillustrates a correct cross-sectional image at the position same as FIG.19E.

As described, the ultrasonic image generating device according to areference example generates a volume image using ultrasonic imagesobtained by scanning from different directions using a ultrasonic probe,and then generates cross-sectional images of arbitrary cross-sectionsusing the volume image. Therefore, even though the target objects can beseparated on the y-z plane shown in FIG. 19C, a correct cross-sectionalimage may not be generated as shown in FIG. 19E. In such a manner, thecross-sectional images obtained by the ultrasonic image generatingdevice according to a reference example are synthesized from the volumeimage constructed without considering the direction dependency of theresolution of the ultrasonic images. Therefore, the ultrasonic imagegenerating device according to a reference example has a degradedaccuracy due to the influence of the decreased resolution in the C-planedirection.

One non-limiting and exemplary embodiment provides an ultrasonic imagegenerating device with an increased accuracy.

In one general aspect, the techniques disclosed here feature anultrasonic image generating device which generates a cross-sectionalimage of a specific cross-section of a subject from a plurality ofultrasonic images obtained by scanning the subject from a plurality ofdirections using an ultrasonic probe, and includes: a cross-sectionposition identifying unit which obtains cross-section informationindicating a position and an orientation of the specific cross-section;a positional information obtaining unit which obtains positionalinformation including a position and an orientation of each of theultrasonic images of the subject; a reference image selecting unit whichselects at least one of the ultrasonic images as a reference image, theat least one of the ultrasonic images having a distance from thespecific cross-section that is less than a first threshold and anorientation difference from the specific cross-section that is less thana second threshold; and a cross-sectional image generating unit whichgenerates the cross-sectional image using the reference image.

With this configuration, the ultrasonic image generating deviceaccording to an exemplary embodiment disclosed herein generatescross-sectional images using ultrasonic images each having smallorientation difference from a specific cross-section. As a result, theultrasonic image generating device can generate cross-sectional imagesusing high-resolution ultrasonic images, thereby increasing accuracy ofthe cross-sectional images.

It also may be that the specific cross-section includes a region ofinterest, and the reference image selecting unit selects, as thereference image, an ultrasonic image having a distance from a pointincluded in the region of interest in the specific cross-section that isless than the first threshold and an orientation difference from thespecific cross-section that is less than the second threshold.

With this configuration, the ultrasonic image generating deviceaccording to an exemplary embodiment disclosed herein can increase theaccuracy of the region of interest that is particularly important.

It also may be that the reference image selecting unit selects anultrasonic image as the reference image from the ultrasonic images, foreach of a plurality of regions obtained by dividing the specificcross-section, the ultrasonic image having a distance from the regionthat is less than the first threshold and an orientation difference fromthe specific cross-section that is less than the second threshold, andthe cross-sectional image generating unit generates an image of each ofthe regions using the reference image selected for the region.

With this configuration, the ultrasonic image generating deviceaccording to an exemplary embodiment disclosed herein can increase theaccuracy of the cross-sectional images by selecting reference images forrespective regions included in the specific cross-sections.

It also may be that the reference image selecting unit selects anultrasonic image as the reference image from the ultrasonic images foreach of the regions, the ultrasonic image having a distance from acentral point of the region that is less than the first threshold and anorientation difference from the specific cross-section that is less thanthe second threshold.

It also may be that the positional information obtaining unit obtains aposition and an orientation of the ultrasonic probe to calculate thepositional information based on the position and the orientation of theultrasonic probe.

It may also be that the positional information obtaining unit furtherobtains a direction of ultrasonic waves emitted from the ultrasonicprobe to calculate the positional information based on the direction ofthe ultrasonic waves and the position and the orientation of theultrasonic probe.

With this configuration, the ultrasonic image generating deviceaccording to an exemplary embodiment disclosed herein can obtain thepositional information of the ultrasonic images generated by using, forexample, a three-dimensional vibrating probe.

It also may be that the first threshold is less than or equal to aresolution in a C-plane that is parallel to a scanning direction of theultrasonic probe, and the second threshold is less than or equal to 30degrees.

With this configuration, the ultrasonic image generating deviceaccording to an exemplary embodiment disclosed herein can increase theaccuracy of the cross-sectional images.

It may also be that when the ultrasonic images do not include theultrasonic image having a distance from the specific cross-section thatis less than the first threshold and an orientation difference from thespecific cross-section that is less than the second threshold, thecross-sectional image generating unit generates the cross-sectionalimage using an ultrasonic image which is included in the ultrasonicimages and has a smallest distance from the specific cross-section.

With this configuration, the ultrasonic image generating deviceaccording to an exemplary embodiment disclosed herein can generatecross-sectional images even when no ultrasonic image meets theconditions for the reference images.

It may also be that a volume generating unit generates a volume imagefrom the ultrasonic images, wherein the cross-section positionidentifying unit generates the cross-section information indicating thespecific cross-section identified by a user with respect to the volumeimage.

The configuration allows a user to easily select specificcross-sections.

It may also be that the reference image selecting unit 0) selects, asthe reference image, an ultrasonic image having a distance from thespecific cross-section that is less than the first threshold and anorientation difference from the specific cross-section that is less thanthe second threshold, when the specific cross-section includes a regionof interest, and (ii) selects the reference image based only on thedistance from the specific cross-section out of the distance from thespecific cross-section and the orientation difference from the specificcross-section, when the specific cross-section does not include theregion of interest.

With the configuration, the ultrasonic image generating device accordingto an exemplary embodiment disclosed herein can increase the accuracy ofthe region of interest which is particularly important, and also canreduce calculation amount relative to less important portions.

It may also be that the reference image includes a plurality ofreference images, and the cross-sectional image generating unit (i)generates a pixel value of a pixel included in the cross-sectional imageby multiplying a pixel value of a pixel included in each of thereference images by a weighting coefficient and summing resulting pixelvalues, and (ii) increases the weighting coefficient for a referenceimage having a smaller orientation difference from the specificcross-section among the reference images.

With this configuration, the ultrasonic image generating deviceaccording to an exemplary embodiment disclosed herein can increase theaccuracy of the cross-sectional images by using a plurality of referenceimages,

It may also be that the cross-sectional image generating unit increasesthe weighting coefficient for a reference image having a smallerorientation difference from the specific cross-section, the referenceimage being included in the reference images and having a distance fromthe specific cross-section that is less than a third threshold.

Moreover, the ultrasonic image generating device according to anexemplary embodiment disclosed herein generates a cross-sectional imagefrom a plurality of Doppler images each of which indicates blood flow,the cross-sectional image indicating blood flow in a specificcross-section of a subject, the Doppler images being obtained byscanning the subject from a plurality of directions using an ultrasonicprobe. The ultrasonic image generating device includes; a cross-sectionposition identifying unit which obtains cross-section informationindicating a position and an orientation of the specific cross-section;a blood flow direction obtaining unit which obtains blood flowinformation indicating a direction of the blood flow in the specificcross-section; a positional information obtaining unit which obtainspositional information including a position and an orientation of eachof the Doppler images of the subject; a reference image selecting unitwhich selects at least one of the Doppler images as a reference image,the at least one of the Doppler images having a distance from thespecific cross-section that is less than a first threshold and anorientation different from the direction of the blood flow by less thana second threshold; and a cross-sectional image generating unit whichgenerates the cross-sectional ge using the reference image.

With this configuration, the ultrasonic image generating deviceaccording to an exemplary embodiment disclosed herein generatescross-sectional images using ultrasonic images each having a smallorientation difference from the direction of the blood flow. With thisconfiguration, the ultrasonic image generating device can generatecross-sectional images using highly sensitive Doppler images, therebyincreasing the accuracy of the cross-sectional images.

These general and specific aspects may be implemented not only as anultrasonic image generating device, but also as an image generatingmethod which includes characteristic units as steps, or as a problemcausing a computer to execute the steps. Needless to say, such a programmay be distributed over a computer-readable nonvolatile recording mediumsuch as a compact disc-read only memory (CD-ROM) or a transmissionmedium such as the Internet.

Furthermore, these general and specific aspects may be implemented as asemiconductor integrated circuit (LSI) which includes part or all of thefunctions of the ultrasonic image generating device, or may beimplemented as an ultrasonic diagnostic device including the ultrasonicimage generating device.

Hereinafter, certain exemplary embodiments are described with referenceto the accompanying drawings. Each of the exemplary embodimentsdescribed below shows a general or specific example. The numericalvalues, shapes, materials, structural elements, the arrangement andconnection of the structural elements, steps, the processing order ofthe steps etc. shown in the following exemplary embodiments are mereexamples, and therefore do not limit the scope of the appended Claimsand their equivalents. Therefore, among the structural elements in thefollowing exemplary embodiments, structural elements not recited in anyone of the independent claims are described as arbitrary structuralelements.

Embodiment 1

An ultrasonic image generating device according to Embodiment 1disclosed herein generates cross-sectional images from originalultrasonic images instead of generating cross-sectional images from avolume image. In addition, the ultrasonic image generating devicedetermines reference images used for generating the cross-sectionalimages, based on the distance between the cross-sectional image and theultrasonic image, and the orientations of the cross-sectional image andthe ultrasonic image. As a result, the ultrasonic image generatingdevice according to Embodiment 1 disclosed herein increases accuracy ofthe cross-sectional images.

First, a description is given of a basic configuration of the ultrasonicimage generating device according to Embodiment 1 disclosed herein. FIG.1 is a block diagram of an ultrasonic image generating device 100according to Embodiment 1.

The ultrasonic image generating device 100 shown in FIG. 1 generates across-sectional image 205 of a specific cross-section of a subject froma plurality of ultrasonic images 201 obtained by scanning the subjectfrom different directions using an ultrasonic probe 101. The ultrasonicimage generating device 100 includes: a cross-section positionidentifying unit 111; a positional information obtaining unit 110; areference image selecting unit 196; and a cross-sectional imagegenerating unit 197.

The cross-sectional position identifying unit 111 obtains cross-sectioninformation 202 indicating the position and the orientation of thespecific cross-section.

The positional information obtaining unit 110 obtains positionalinformation 203 including respective positions and orientations of theultrasonic images 201 of the subject. More specifically, the positionalinformation obtaining unit 110 obtains, as the positional information203, probe positional information (the position and the orientation ofthe ultrasonic probe 101) at the time of obtainment of the ultrasonicimages detected by a position sensor such as a camera or a magneticsensor. The positional information obtaining unit 110 may calculate thepositional information 203 using the probe positional information. Theorientation of the ultrasonic probe 101 is the orientation of the planewhich is along the direction of the ultrasonic waves emitted by theultrasonic probe 101 and which is parallel to the array direction of theultrasonic transducers. In other words, the orientation of theultrasonic probe 101 is the orientation of the B-plane.

The reference image selecting unit 196 selects at least one ultrasonicimage 201 from the ultrasonic images 201 as a reference image. Theselected ultrasonic image 201 has a distance from the specificcross-section that is less than a first threshold, and an orientationdifference from the specific cross-section that is less than a secondthreshold.

The cross-sectional image generating unit 197 generates thecross-sectional image 205 using the reference images selected by thereference image selecting unit 196.

Hereinafter, descriptions are given of the ultrasonic image generatingdevice 100 and an image generating method according to Embodiment 1,with reference to the drawings. In the following, a general descriptionis given of the functions of the ultrasonic image generating device 100,with an example of breast examination. FIG. 2A is a diagram showing ausage example of the ultrasonic image generating device 100.

As shown in FIG. 2A, the ultrasonic image generating device 100 obtainsultrasonic images 201 of a breast taken from different directions, byscanning the breast using the ultrasonic probe 101 from differentdirections such as direction (1) and direction (2). Examples of theultrasonic probe 101 that may be used include a linear array probe, athree-dimensional (3D) vibrating probe, and a matrix array probe. Thelinear array probe includes at least one row of ultrasonic transducers,and provides two-dimensional images. The 3D vibrating probe includes onerow of ultrasonic transducers, and continuously generatestwo-dimensional images by the vibration or linear movement of theultrasonic transducers. The 3D vibrating probe providesthree-dimensional images by using the two-dimensional images thusgenerated. The matrix array probe includes transducers that aretwo-dimensionally arranged, and provides three dimensional images. InEmbodiment 1, a description is given of an example where the lineararray probe is used.

The ultrasonic probe 101 is equipped with an optical marker 301. Acamera 302 captures images of the optical marker 301. The ultrasonicimage generating device 100 analyzes the changes of the position and theposture of the optical marker 301 by using the images captured by thecamera 302, to obtain the positional information of the ultrasonic probe101 (hereinafter, referred to as probe positional information) at thetime of obtainment of the ultrasonic signals used for the ultrasonicimage generating device 100 to generate the ultrasonic images 201.Hereinafter, the time when the ultrasonic image generating device 100obtains the ultrasonic signals for generating the ultrasonic images 201is referred to as obtainment timing of the ultrasonic images 201.

The ultrasonic probe 101 and the camera 302 operate in synchronizationwith one another, or operate according to respective known referenceclocks, to match the obtainment timing of the ultrasonic images 201 andthe obtainment timing of the positional information 203. The probepositional information indicates the position and the orientation of theultrasonic probe 101. More specifically, the probe positionalinformation includes six parameters in total which are the positions(corresponds to coordinate values of x, y, and z axes) and orientations(rotation about three respective axes) in the three-dimensional space.

FIG. 2A shows an example where the optical marker 301 is attached to theultrasonic probe 101; however, it may be that the camera 302 is attachedto the ultrasonic probe 101 and the optical marker 301 is arrangedaround the ultrasonic probe 101. In this case, it is desirable to use aplurality of optical markers 301 in order to increase the accuracy ofthe position detection.

FIG. 2B is a volume image 206 of the inside the breast shown in FIG. 2A.When a user identifies a specific cross-section 351 surrounded with adotted line in FIG. 2B, via, for example, a user interface on thedisplay, the cross-sectional image 205 of the specific cross-section 351is generated to be displayed on the display screen of the ultrasonicimage generating device 100, as shown in FIG. 2C.

FIG. 3 is a block diagram of a configuration of the ultrasonic imagegenerating device 100 according to Embodiment 1. The ultrasonic imagegenerating device 100 includes the ultrasonic probe 101, a transmittingunit 102, a receiving unit 103, a transmission and reception controlunit 104, a B-mode processing unit 105, a Doppler processing unit 106, astrain processing unit 107, an image memory 108, an image processingunit 109, a positional information obtaining unit 110, a cross-sectionalposition identifying unit 111, and a display unit 112.

The ultrasonic image generating device 100 according to Embodiment 1 hasfeatures in the operations of the image processing unit 109. Thus, theoperations of the image processing unit 109 will be mainly described inthe following, and descriptions of the other processing units may beomitted. The operations of the respective processing units which receiveand transmit ultrasonic signals and perform B-mode processing or Dopplerprocessing are the same as those of the ultrasonic image generatingdevice 500 according to a reference example. In addition, the samereferential numbers are assigned to the elements similar to those ofFIG. 16,

FIG. 3 illustrates the B-mode processing unit 105, the Dopplerprocessing unit 106, and the strain processing unit 107 as units forprocessing ultrasonic signals provided from the receiving unit 103 whichreceives the ultrasonic signals. However, such configurations are notessential for the ultrasonic image generating device 100. It issufficient that the ultrasonic image generating device 100 includes atleast one of the B-mode processing unit 105, the Doppler processing unit106, and the strain processing unit 107, depending on the types of theimages to be displayed on the display unit 112. It may also be that theultrasonic image generating device 100 does not include the display unit112, and the ultrasonic image generating device 100 provides displayimages to the display unit 112 provided externally.

Furthermore, in Embodiment 1, data which indicates an image or volumeimage is simply referred to as an image and a volume image.

FIG. 4 is a block diagram illustrating a configuration of the imageprocessing unit 109. The image processing unit 109 includes a frameimage input unit 191, a positional information determining unit 192, atable generating unit 193, a positional information memory 194, an imagememory 195, a reference image selecting unit 196, and a cross-sectionalimage generating unit 197.

The frame image input unit 191 obtains ultrasonic images 201 that aretwo-dimensional images, such as B-mode images or Doppler images, storedin the image memory 108, and index numbers 211 of the ultrasonic images201. The index numbers 211 are associated with, for example, theultrasonic images 201. The index numbers 211 are stored in the imagememory 108 with the ultrasonic images 201. The frame image input unit191 stores the obtained ultrasonic images 201 and index numbers 211 intothe image memory 195, and provides the index numbers 211 to thepositional information determining unit 192. In the following, adescription is given of an example where the ultrasonic images 201 areB-mode images.

The positional information determining unit 192 determines thepositional information 212 corresponds to the ultrasonic image 201having the index number 211 based on the positional information 203obtained by the positional information obtaining unit 110. Thepositional information 203 and 212 indicate the position and theorientation of a specific part of the optical marker 301 attached to theultrasonic probe 101 or the ultrasonic probe 101 relative to a knownnormal coordinate. It may be that the image processing unit 109 does notinclude the frame image input unit 191, but the table generating unit193 assigns index numbers to respective images.

Next, the table generating unit 193 associates the positionalinformation 212 of each ultrasonic image 201 (frame) with the indexnumber 211 of each ultrasonic image 201 based on the positionalinformation 212, and generates a positional information table 221indicating the association. The positional information memory 194 storesthe positional information table 221 generated by the table generatingunit 193. The positional information memory 194 does not have to storethe association as a table as long as the positional information memory194 stores the positional information 212 of the ultrasonic image 201 inassociation with the index number 211 of the ultrasonic image 201. Thepositional information in the positional information memory 194 may bethe same as the positional information 212, and also may be valuestransformed into different coordinate systems. One example of thedifferent coordinate systems is a three-dimensional coordinate systemused by the image processing unit 109 or the display unit 112.

The reference image selecting unit 196 determines frames (hereinafter,referred to as reference images) to be referred to for synthesizingrespective pixel values of the cross-sectional image 205, with referenceto the positional information table 221. The reference image selectingunit 196 provides, to the cross-sectional image generating unit 197, theindex numbers of the determined reference images as reference imageinformation 213.

The cross-sectional image generating unit 197 obtains the referenceimages indicated by the reference image information 213 from the imagememory 195. The cross-sectional image generating unit 197 thenadaptively applies weighting to pixels in the reference images andcombining pixel values to generate the cross-sectional image 205. Thecross-sectional image generating unit 197 provides the generatedcross-sectional image 205 to the display unit 112.

For displaying the volume image 206 on the display unit 112, the imageprocessing unit 109 may additionally include a volume generating unit199 and a volume memory 198. In other words, the image processing unit109 does not have to include the volume generating unit 199 and thevolume memory 198.

The volume generating unit 199 constructs the volume image 206 based onthe positional information 203 and the ultrasonic images 201, and storesthe volume image 206 in the volume memory 198. The display unit 112 thenobtains the volume image 206 from the volume memory 198, and displaysthe obtained volume image 206.

When a user identifies the specific cross-section 351 with respect tothe displayed volume image 206, the cross-sectional position identifyingunit 111 generates the cross-section information 202 indicating theposition and the orientation of the specific cross-section 351. Thecross-sectional image generating unit 197 then generates respectivepixel values of the specific cross-section 351 indicated by thecross-section information 202, using the reference images selected bythe reference image selecting unit 196.

FIG. 5 is a flowchart of processing for synthesizing cross-sectionalimages performed by each processing unit of the image processing unit109.

First, the frame image input unit 191 obtains the ultrasonic image 201generated from the ultrasonic signals obtained by the ultrasonic probe101 (S101).

Next, the positional information obtaining unit 110 obtains, based onthe output signals from the position sensor or the like, the positionalinformation 203 corresponding to the ultrasonic image 201 (S102). Here,when the ultrasonic signals used for generating the ultrasonic image 201are received, the position and the orientation of the ultrasonic probe101 are obtained as the positional information 203.

The table generating unit 193 then associates the ultrasonic image 201and the positional information 203 (212) and generates the positionalinformation table 221 indicating the association (S103). It may be thatthe image processing unit 109 does not generate the positionalinformation table 221, but simply add the positional information 203 toeach ultrasonic image 201 as index information. It may also be that theobtainment timing of the ultrasonic image 201 does not strictly matchthe obtainment timing of the positional information 203. For example,the positional information obtaining unit 110 may obtain the positionalinformation 203 immediately after the obtainment of the ultrasonic image201.

The cross-sectional position identifying unit 111 obtains, for example,the cross-section information 202 indicating the specific cross-sectionidentified by the user (S104).

The image processing unit 109 then generates the pixel values in thespecific cross-section identified by the cross-section information 202.This generation processing is performed for each pixel or for eachregion including a group of pixels (however, the region is smaller thanthe specific cross-section). The following describes an example wherethe generation processing is performed for each pixel.

First, the image processing unit 109 selects a pixel to be processed(hereinafter, referred to as a target pixel) included in the specificcross-section (S105).

The reference image selecting unit 196 then calculates the position inthe three-dimensional space of the target pixel in the specificcross-section. The reference image selecting unit 196 then selectsreference images based on the position of the target pixel and theposition of each ultrasonic image 201 (S106). The processing forselecting the reference images will be described later in detail.

The cross-sectional image generating unit 197 then generates (S107) thepixel value of the target pixel using the pixel values of the referenceimages selected in Step S106. The details of the processing will bedescribed later.

In the case where the processing of Steps S105 to S107 have not beencompleted for all of the pixels in the specific cross-section (NO inS108), a new target pixel is selected in Step S105, and the processingafter Step S106 is performed on the selected target pixel.

In the case where the processing of Steps S105 to S107 have beencompleted for all of the pixels in the specific cross-section (Yes inS108), the cross-sectional image generating unit 197 generates thecross-sectional image 205 of the specific cross-section, using the pixelvalue of each pixel generated in the above processing (S109).

The following describes the processing for selecting the referenceimages (S106). FIG. 6 is a flowchart of a detail of the operations ofthe reference image selecting unit 196.

First, the reference image selecting unit 196 calculates the distancebetween the target pixel and each ultrasonic image 201 (S121). Next, thereference image selecting unit 196 determines whether or not there areany ultrasonic images 201 having a distance that is less than thresholdT1 (S122).

When there are ultrasonic images 201 each having a distance that is lessthan the threshold T1 (Yes in S122), the reference image selecting unit196 selects the ultrasonic images 201 as candidate reference images(S123).

Here, it is defined that the distance between the target pixel and theultrasonic image 201 is the length of a perpendicular line drawn fromthe target pixel mapped into the three-dimensional space to theultrasonic image 201. When the processing is performed for each region,the distance is the distance between the target region and theultrasonic image 201. For example, the distance is the length of aperpendicular line drawn from the central point of the target region tothe ultrasonic image 201. When the specific cross-section or the targetregion includes a region of interest (ROI), the distance may be adistance between a point included in the ROI and the ultrasonic image201. When a tumor in the specific cross-section is observed, the ROI isa tumor and the neighboring region. The ROI is set by a user, orautomatically set by image processing techniques such as boundaryextraction or object recognition.

Here, the ultrasonic image 201 used as a reference mage refers to all orpart of the frames having index numbers stored in the positionalinformation table 221. It is desirable that the threshold T1 is set tobe, for example, smaller than the beam diameter at the position whereultrasonic waves spread least (focus point). It is also desirable thatthe threshold T1 is set to be a value equal to or less than theresolution in the C-plane at the position of the target pixel. As aresult, it is possible to generate higher-resolution images compared tothe conventional images.

Next, the reference image selecting unit 196 calculates the anglebetween the specific cross-section and each candidate reference image(S125). The reference image selecting unit 196 then determines whetheror not the candidate reference images include any frames having anorientation difference from the specific cross-section that is less thanthreshold T2 (S126). Here, it is desirable that the threshold T2 is avalue equal to or less than 30 degrees.

When there are candidate reference images each having the orientationdifference that is less than the threshold T2 (Yes in S126), thereference image selecting unit 196 selects, as reference images, thecandidate reference images having the orientation difference that isless than the threshold T2 (S127).

When there is no candidate reference image having the orientationdifference that is less than the threshold T2 (No in S126), thereference image selecting unit 196 selects the candidate referenceimages determined in S123, as reference images (S128).

When there is no ultrasonic image 201 having the distance that is lessthan the threshold T1 (No in S122), the reference image selecting unit196 determines that there is no reference image (S124), and endssearching for the reference images.

It has been described that the reference image selecting unit 196 uses,for determining the reference images, two parameters that are thedistance between the target pixel and the ultrasonic image 201 and theorientation difference between the specific cross-section and theultrasonic image 201; however, other parameters may be combined. Thefollowing describes examples of three other parameters that are themovement speed of the ultrasonic probe 101 at the time of obtainment ofthe ultrasonic images 201, focus positions in the ultrasonic images 201,and frequency distribution in the ultrasonic images 201.

First, a description is given of a case where the movement speed isused. When the movement speed is faster relative to the frame rate atthe time of the obtainment of the ultrasonic images 201, the ultrasonicprobe 101 moves while the ultrasonic images 201 are being obtained,resulting in so called motion blur. As a result, the resolution of theultrasonic images 201 decreases. It can be defined that the movementspeed of the ultrasonic probe 101 is the movement distance of theultrasonic probe 101 in a unit time. Thus, the movement speed can becalculated from the interval between neighboring frames and the framerate.

For determining the reference images, the reference image selecting unit196 preferentially uses the ultrasonic images 201 having the motion blurwithin the acceptable range, or the ultrasonic images 201 having themovement speed that is equal to or less than the threshold. In thiscase, the table generating unit 193 may generate the positionalinformation table 221 including information of the movement speed of theultrasonic probe 101.

Next, a description is given of a case where the focus positioninformation is added as a condition for determining the referenceimages. The image quality of the ultrasonic image 201 varies dependingon the convergence position of ultrasonic waves emitted from theultrasonic probe 101. In other words, in the ultrasonic image 201, thedepth near the convergence position is in focus, thereby providinghigh-resolution images. The resolution decreases due to being out offocus, the further the distance from the convergence position is. Thereference image selecting unit 196 preferentially selects pixels nearthe convergence position when reference images are determined from thepixels of the ultrasonic image 201. The convergence position may beobtained as a parameter value of the ultrasonic probe 101 at the time ofthe obtainment of the ultrasonic image 201. In this case, the positionalinformation table 221 may further include convergence positioninformation. Since the resolution of ultrasonic waves decreases as thedepth increases, the depth of the pixels may also be used as aparameter. More specifically, the reference image selecting unit 195preferentially selects pixels having narrow depth for determining thereference images.

Lastly, a description is given of the case where frequency distributionin the ultrasonic image 201 is added as a condition for determining thereference images. The objective of the selection of the reference imagesis to select the ultrasonic images 201 having high resolution near atarget pixel. The reference image selecting unit 196 performs frequencyanalysis on the ultrasonic images 201 by, for example, fast Fouriertransformation, and preferentially selects, as a reference image, theultrasonic images 201 including a large amount of high frequencycomponents. In this case, the positional information table 221 mayinclude rate of the high frequency components in each ultrasonic image201 (for example, average frequency).

In addition, the reference images may be determined in view ofcontinuity of pixels. This is because the result of the combining may bediscontinuous when each pixel has a different reference image. Thus, thereference image selecting unit 196 may preferentially select, as areference image for the target pixel, the reference image selected for aneighboring pixel of the target pixel. More specifically, in the casewhere a first reference image selected for a target pixel is differentfrom a second reference image used for a neighboring pixel of the targetpixel and where the distance or the orientation difference between thefirst reference image and the second reference image is smaller than apredetermined value, the reference image selecting unit 196 may selectthe second reference image as a reference image for the target pixel.

Selecting a reference image for each pixel requires a large amount ofcalculations. In the case where cross-sectional images are displayedwhile being switched in real-time, it is effective to reduce the amountof calculation. Thus, a reference image may be selected for eachspecific cross-section or each region within the specific cross-section.Here, the evaluation of the distance and the orientation may beperformed for the pixel corresponding to the central point of thespecific cross-section or of each region within the specificcross-section.

For observing a tumor within the specific cross-section, the ROIincluding the tumor and the neighboring region is particularlyimportant. Thus, it may be that the reference image selecting unit 196selects reference images for the ROI by smaller particle size, such asin a unit of pixel, and select reference images for regions other thanthe ROI by larger particle size, such as in a unit of region.

In FIG. 6, the reference image selecting unit 196 selects referenceimages according to the angle after selecting the candidate referenceimages according to the distance; however, the order may be inverse.Furthermore, some processing may be performed in parallel.

Hereinafter, a detailed description is given of the processing forgenerating the pixel value of a target pixel (S107). FIG. 7 is aflowchart of the detailed processing for generating the pixel value ofthe target pixel performed by the cross-sectional image generating unit197.

First, the cross-sectional image generating unit 197 determines whetheror not there are any reference images for a target pixel (S141).

When there are reference images (YES in S141), the cross-sectional imagegenerating unit 197 calculates the importance score of each referenceimage by performing a weighted sum operation on a first score determinedbased on the distance between the target pixel and the reference imageand on a second score determined based on an orientation differencebetween the specific cross-section and the reference image (S142) Thecross-sectional image generating unit 197 sets the first score and thesecond score such that the weight of the first score increases as thedistance decreases and that the weight of the second score increases asthe orientation difference decreases. When the reference images do notinclude any frames having the orientation difference that is less thanthe threshold T2, the cross-sectional image generating unit 197calculates the importance score based only on the first score. Forexample, the weight of the first score is the same as that of the secondscore.

When an ultrasonic image obtained near a target position is emphasized,it suffices to increase the weight of the first score (the coefficientby which the first score is multiplied is set to be greater than thecoefficient by which the second score is multiplied). When an ultrasonicimage that is nearer to the B-plane than to the target pixel isemphasized, it suffices to increase the weight of the second score (thecoefficient by which the second score is multiplied is set to be greaterthan the coefficient by which the first score is multiplied).

Out of the selected reference images and the reference images eachhaving a distance from the target pixel that is less than a thirdthreshold, the weighting coefficient may be increased for a referenceimage having a smaller orientation difference from the specificcross-section. Here, the third threshold is smaller than the firstthreshold T1. As a result, it is possible to obtain higher-qualitycross-sectional images than ultrasonic images according to a referenceexample.

Next, the cross-sectional image generating unit 197 selects referencepixels used for generating the target pixel, based on the importancescore of each reference image (S143). Lastly, the cross-sectional imagegenerating unit 197 calculates the pixel value of the target pixel byperforming weighted sum operation on the pixel values of the referencepixels selected in Step S143 using the importance score of the referenceimages which include the reference pixels (S144).

When there is no reference image in Step S141 (NO in S141), thecross-sectional image generating unit 197 does not combine the pixelvalues for the target pixel, but assigns a predetermined pixel value,for example, “0” to the target pixel (S145).

As shown in FIG. 8, when there is no reference image (NO in S141), thecross-sectional image generating unit 197 may generate a target pixelusing the pixel value of the ultrasonic image 201 having smallestdistance from the target pixel (S145A).

It may also be that the cross-sectional image generating unit 197interpolates and generates a target pixel by using the pixel values ofthe prior calculated pixel located near the target pixel.

Furthermore, the generated cross-sectional image 205 may distinguish thesynthesized pixels from the non-synthesized pixels because of absence ofthe reference images, by, for example, displaying them in differentcolors.

For performing the combining, at least one pixel of the ultrasonic image201 needs to be present within a range of the distance from the targetpixel that is less than the threshold T1. Thus, some specificcross-sections may include a number of pixels that cannot besynthesized. Therefore, as shown in FIG. 2B, it may be that a volumeimage constructed from the ultrasonic images 201 is displayed indicatingthe cross-sections that can be synthesized. In other words, it may bethat voxels having the pixels of the ultrasonic image 201 within a rangeof the distance that is less than the threshold T1 are identified asvoxels that can be combined, in order to be distinguished from voxelsthat cannot be combined. For example, different colors may be used fordisplaying the voxels that can be combined and the voxels that cannot becombined.

When the specific cross-section is identified by a user, or isautomatically set, it is desirable that a specific cross-section isselected with reference to the combinable or uncombinable informationsuch that the specific cross section includes at least two or morepixels that can be synthesized. Alternatively, as a simpler method, adisplay may be performed such that voxels which include pixels of theultrasonic images 201 are distinguished from voxels which include nopixel of the ultrasonic images 201.

Furthermore, when the cross-sectional position identifying unit 111identifies the specific cross-section, the display unit 112 may present,to the user, information indicating which pixel can be synthesized andcannot be synthesized in the specific cross-section. When the rate ofthe pixels that cannot be synthesized in the specific cross-section orin the ROI in the specific cross-section exceeds a predetermined rate,information may be presented which prompt the user to identify adifferent neighboring cross-section.

FIG. 9A, FIG. 9B, and FIG. 9C are diagrams for describing theadvantageous effects of the ultrasonic image generating device 100according to Embodiment 1.

Here, it is assumed that two cubes, which are imaging target objects,are placed at a distance in the y-axis direction, as shown in FIG. 19A.It is also assumed that the distance between the two cubes is smallerthan the spatial resolution in the C-plane that is parallel to thescanning direction of the ultrasonic probe 101, and greater than thespatial resolution in the B-plane that is perpendicular to the scanningdirection of the ultrasonic probe 101.

A plurality of ultrasonic images 201 are generated by scanning thetarget objects in two directions that are y-axis direction and x-axisdirection. FIG. 9A and FIG. 9B each shows the ultrasonic images 201generated by scanning in the y-axis direction and the x-axis direction.In FIG. 9B, the specific cross-section 351 is identified. The specificcross-section 351 is not identical to any one of the ultrasonic images201.

In this case, the reference image selecting unit 196 selects thereference image 361 located immediately preceding the specificcross-section 351 and the reference image 362 located immediatelysucceeding the specific cross-section 351, based on the distance and theorientation difference from the specific cross-section 351.

FIG. 9C shows two reference images 361 and 362, and the cross-sectionalimage 205 of the specific cross-section generated from the two referenceimages 361 and 362. As shown in FIG. 9C, two target objects areseparated in the cross-sectional image 205. The reference images 361 and362 correspond to the B-plane. By combining pixel values of thereference images 361 and 362 which have resolution of the B-plane, thecross-sectional image 205 having resolution close to that of the B-planecan be obtained.

On the other hand, as described earlier, two target objects cannot beseparated in the cross-sectional image generated by the ultrasonic imagegenerating device according to a reference example.

As described, the ultrasonic image generating device 100 according toEmbodiment 1 disclosed herein is capable of generating specificcross-sectional images with high resolution. In other words, theultrasonic image generating device 100 is capable of increasing theaccuracy of the cross-sectional image 205.

It has been described that scanning with the ultrasonic probe 101 islinearly performed in the x-direction and the y-direction in FIG. 9A toFIG. 9C for ease of explanation; however, the same advantageous effectscan be obtained also in the case where scanning with the ultrasonicprobe 101 is freely performed in any directions by a probe user. In thiscase, even though the obtainment order of the ultrasonic images 201 areused (even though immediately preceding and immediately succeedingframes are simply used) for synthesizing respective pixels in thespecific cross-section 351, the specific cross-section 351 does not havehigher resolution. Thus, Embodiment 1 provides more marked effects insuch a case.

FIG. 10 is a diagram illustrating another example of the specificcross-section 351. When the specific cross-section 351 shown in FIG. 10is identified, four reference images 371 to 374 are selected. The pixelsof the reference regions 381 to 384 included in the four referenceimages 371 to 374 are used as reference pixels for the synthesis of thetarget pixels.

As described above, the ultrasonic image generating device 100 accordingto Embodiment 1 disclosed herein selects reference images used for thecombining, based on the similarity degree of the positional information203 such as the distance between the specific cross-section 351 and theultrasonic image 201 and their orientations. As a result, when there areultrasonic images 201 having the positional information 203 close tothat of the specific cross-section 351, it is possible to generate across-sectional image 205 having resolution close to that of theB-plane.

Hereinafter, a Variation of Embodiment 1 is described.

First, a description is given of the operations performed when the 3Dvibrating probe or the matrix array probe is used as the ultrasonicprobe 101.

When the 3D vibrating probe is used, ultrasonic probe elements arrangedin line vibrate in the probe. As a result, two-dimensional ultrasonicimages can be continuously obtained. With use of the ultrasonic images,it is possible to create images of a three-dimensional region beneaththe probe. The obtained two-dimensional ultrasonic images are the sameas the images obtained by the linear array probe. By assuming thesetwo-dimensional ultrasonic images as the ultrasonic images 201, theprocessing same as the processing above can be performed. It is to benoted that the positional information 203 of the ultrasonic image 201depends on the position and the orientation of the ultrasonic probeelements (ultrasonic transducers) in the probe at the time of theobtainment of the ultrasonic image 201, in addition to the probepositional information. Accordingly, the positional informationobtaining unit 110 obtains information on the position and theorientation of the ultrasonic probe elements, in addition to the probepositional information (the position and the orientation of theultrasonic probe). The positional information obtaining unit 110calculates the positional information 203 of the ultrasonic image 201 byadding, as offset values, the position and the orientation of theultrasonic probe elements to the position and the orientation of theultrasonic probe 101.

When the matrix array probe is used, the ultrasonic probe elements donot physically move in the probe, but the matrix array probe is the sameas the 3D vibrating probe in that images of the 3D region beneath theprobe are created. Thus, the matrix array probe can be treated in thesame way as the 3D vibrating probe by dividing the created 3D regionimage into a plurality of frames, and taking into account the positionalinformation of each frame.

In the above description, the diagnostic target is the breast; however,the diagnostic target may be parts or organs other than the breast, suchas liver, carotid artery, or prostate gland. FIG. 11 is a diagramillustrating an example of a volume image in the case where thediagnostic target is the carotid. In this case, the ROI is a plaque 391formed in the carotid and the neighboring regions Here, the plaquerefers to a protruded lesion where tunica intima and tunica media of ablood vessel are thickened. The plaques have various forms, such asthrombus, fatty plaque, or fibrous plaque, and may cause carotidstenosis, carotid occlusion, cerebral infarction, or cerebral ischemia.As arteriosclerosis develops, plaque is readily formed. Arteriosclerosisis considered to systemically develop; and thus, superficial carotidartery is mainly measured for determining the presence or absence ofplaque.

In the above description, optical units such as the camera and theoptical marker are used as a unit for obtaining the positionalinformation 203; however, any other units may be used such as a magneticsensor, an acceleration sensor, a gyro sensor, or a robotic arm.Different types of units for obtaining positional information may beused in combination in a case where a single unit provides insufficientperformance. One example is a case where the optical marker is hiddenbehind a user's hand or the like, causing the optical marker to be inthe blind angle of the camera and resulting in not allowing the opticalunit to provide positional information. The positional information isnot limited to six parameters of the position and the orientation. Forexample, in the case where the movement direction is limited to acertain axis, only necessary parameters may be obtained and used.

The above description describes the method where the ultrasonic imagegenerating device 100 displays the volume image 206, and the useridentifies a specific cross-section from the volume image 206; however,the specific cross-section may be identified by any other methods. Forexample, it may be that scanning with the ultrasonic probe 101 isperformed by a method such as a freehand scanning, and then theultrasonic image generating device 100 displays respective B-planeimages. A user identifies the B-plane image which shows the ROI from thedisplayed B-plane images. Then, the ultrasonic image generating device100 may identify a specific cross-section such that an image of aneighboring region (for example, region having an angle of 0 degree ormore and less than 360 degrees) of the identified B-plane image.

It may also be that the ultrasonic image generating device 100 adoptsthe image generating method according to Embodiment 1 when the specificcross-section includes the ROI, and select reference images simply basedonly on the information of distance from the ROI when the specificcross-section does not include the ROI.

FIG. 12 is a flowchart of the operations of the reference imageselecting unit 196 in this case. The processing shown in FIG. 12includes Step S129 in addition to the processing shown in FIG. 6. Morespecifically, the reference image selecting unit 196 determines whetheror not the specific cross-section includes the ROI after selecting thecandidate reference images in Step S123 (S129).

When the specific cross-section includes the ROI (Yes in S129), thereference image selecting unit 196 selects the reference imagesaccording to the angle between each candidate reference image and thespecific cross-section, in the same manner as in FIG. 6 (S125 to S128).When the specific cross-section includes the ROI (Yes in S129), thereference image selecting unit 196 selects the candidate referenceimages as reference images (S128) In other words, when the specificcross-section identified in the volume image 206 includes the ROI, thereference image selecting unit 196 selects the reference images usingthe information of the distance from the specific cross-section, and theinformation of the orientation difference from the specificcross-section. When the specific cross-section does not include the ROI,the reference image selecting unit 196 selects the reference imagesusing only the distance information, without using the information oforientation difference from the specific cross-section.

For displaying the volume image 206 such that the inside of the volumeimage 206 is transparently viewed, cutting out only the neighboringregion of the ROT increases visibility of the ROT. Thus, the ultrasonicimage generating device 100 may generate the volume image 206 by cuttingout only the neighboring region of the ROI for display.

In Embodiment 1, one or more ultrasonic images are extracted which havethe distance and the angle difference from a target pixel that are equalto or less than a threshold, and each of the extracted ultrasonic imagesis weighed before being used; however, all of the extracted pixels donot need to be used. For example, in the case where scores are set toeach of the extracted ultrasonic images, only some of the ultrasonicimages which have higher matching degree may be used.

In addition, it may be that the ultrasonic image generating device 100determines images which have similar position and orientation from amongthe ultrasonic images 201 stored in the image memory 108 or 195, and oneof the similar images may be deleted. As a result, the amount of theimage memory 108 or 195 may be reduced.

Furthermore, it may be that the ultrasonic image generating device 100stores only the ultrasonic images 201 which include the ROI in the imagememory 195. As a result, the amount of the image memory 195 can bereduced.

Furthermore, the division between the ultrasonic image generating device100 (main unit) and the ultrasonic probe 101 shown in FIG. 3 is merelyan example, and the present disclosure is not limited to this example.For example, it may be defined that a system which includes theultrasonic probe 101 and the main unit (the ultrasonic image generatingdevice 100 shown in FIG. 3) is an ultrasonic image generating device. Itmay also be that the ultrasonic probe 101 includes part of theprocessing units included in the main unit.

The example has been described where B-mode images are mainly used asthe ultrasonic images 201; however, it may be that Doppler images(Doppler data) which indicate blood flow or the like may be used insteadof the B-mode images.

FIG. 13 is a block diagram schematically illustrating a configuration ofan ultrasonic image generating device 100A in this case.

The ultrasonic image generating device 100A generates a cross-sectionalimage 205A indicating blood flow in the specific cross-section of asubject from a plurality of Doppler images 201A which are obtained fromthe scanning of the subject from different directions using theultrasonic probe 101, and which indicate the blood flow (indicate theflow velocity and direction). The ultrasonic image generating device100A includes a cross-sectional position identifying unit 111A, a bloodflow direction obtaining unit 121, a positional information obtainingunit 110A, a reference image selecting unit 196A, and a cross-sectionalimage generating unit 197A.

The cross-sectional position identifying unit 111A obtains cross-sectioninformation 202A indicating the position of the specific cross-section.

The blood flow direction obtaining unit 121 obtains blood flowinformation 231 which indicates the direction of the blood flow in thespecific cross-section. The information of the blood flow direction canbe obtained by using, for example, a method specified by a user, or amethod where Doppler images or B-mode images are analyzed toautomatically detect the blood vessel running position and direction.

The positional information obtaining unit 110A obtains positionalinformation 203A including respective positions and orientations of theDoppler images 201A of the subject.

The reference image selecting unit 196A selects at least one of theDoppler images 201A as a reference image. The selected Doppler images201A each has a distance from the specific cross-section that is lessthan a first threshold, and has an orientation different from thedirection of the blood flow by less than a second threshold.

The cross-sectional image generating unit 197 generates thecross-sectional image 205A using the reference images.

As shown in FIG. 14, measurement sensitivity varies depending on thedifference between the orientation of the ultrasonic probe 101 and thedirection of the blood flow. More specifically, as the differencebetween the direction of the blood flow and the direction of theultrasonic waves emitted from the ultrasonic probe 101 decreases, thesensitivity increases. As a result, the accuracy of the cross-sectionalimage 205A can be increased by generating the cross-sectional image 205Ausing the Doppler images 201A each having a an orientation differentfrom the direction of the blood flow by less than the second threshold.

Detailed configuration of the ultrasonic image generating device 100Aare the same as the ultrasonic image generating device 100 with the“orientation of the specific image” being replaced with the “directionof the blood”; and thus, their detailed description are not repeated.

The ultrasonic image generating device and method according to thepresent disclosure have been described based on Embodiment 1; however,the present disclosure is not limited to the embodiment. The presentdisclosure includes variations came up by those in the art applied inthe present embodiments in a range of the arguments disclosed herein.

Embodiment 2

The processing described in Embodiment 1 can be easily performed in anindependent computer system by recording a program for implementing theimage generating method described in Embodiment 1 on a recording mediumsuch as a flexible disk.

FIG. 15A to FIG. 15C each is a diagram illustrating a case where theimage generating method according to Embodiment 1 is implemented in acomputer system, using the program recorded on the recording medium suchas a flexible disk.

FIG. 15A illustrates an example of a physical format of the flexibledisk that is a recording medium body. FIG. 15B illustrates an externalfront view and a cross-sectional view of a flexible disk and theflexible disk. A flexible disk RD is contained in a case F. A pluralityof tracks Tr are formed concentrically on the surface of the disk fromthe periphery into the inner radius of the disk. Each track Tr isdivided into 16 sectors Se in the angular direction. Accordingly, in theflexible disk FD which stores the program, the program is recorded onsectors assigned to the flexible disk FD.

FIG. 15C illustrates a structure for recording and reproducing theprogram on the flexible disk FD. When the program for implementing theimage generating method is recorded on the flexible disk FD, thecomputer system Cs writes the program on the flexible disk FD via aflexible disk drive FDD. When the image generating method is constructedin the computer system Cs using the program on the flexible disk FD, theprogram is read out from the flexible disk FD using the flexible diskdrive FDD and is transferred to the computer system Cs.

The above description is given on an assumption that a recording mediumis a flexible disk, but an optical disk may be used instead. Inaddition, the recording medium is not limited to the flexible disk andthe optical disk. As long as the program is recorded, any recordingmedium may be used, such as an IC card and a ROM cassette.

The block such as the image processing unit 109 in FIG. 3 is typicallyimplemented as a Large Scale Integration (LSI) that is an integratedcircuit. The LSIs may be separately made into one chip, or each LSI maybe partly or entirely made into one chip.

The LSI may also be referred to IC, system LSI, super LSI, or ultra LSIdepending on the degree of integration.

Moreover, ways to achieve integration are not limited to the LSI. Adedicated circuit or a general-purpose processor may also achieve theintegration. For example, a dedicated circuit for graphics such as agraphic processing unit (GPU) may be used. Field Programmable Gate Array(FPGA) that can be programmed after manufacturing an LSI or areconfigurable processor that allows re-configuration of the connectionor configuration of a circuit cell in an LSI can be used for the samepurpose.

Furthermore, in the future, with advancement in semiconductortechnology, a brand-new technology may replace LSI. The functionalblocks may be integrated using such a technology. The possibility isthat the present disclosure is applied to biotechnology.

Furthermore, at least part of the ultrasonic image generating deviceaccording to the above exemplary embodiments and the functions of thevariations may be combined.

Furthermore, the numbers cited above are used simply to specificallydescribe the present disclosure, and the present disclosure is notlimited thereto.

The divisions of the functional blocks in the block diagrams are anexample. It may be that a plurality of functional blocks are implementedas a single functional block, one functional block is divided intoblocks, or part of the functions is moved to other functional blocks.The functions of the functional blocks having similar functions may beprocessed by a single hardware or software in parallel or in atime-sharing manner.

The described executing order of the steps is merely an example forspecifically describing the present disclosure, and the order is notlimited thereto. Part of the steps may be executed simultaneously (inparallel) with other steps.

Those skilled in the art will readily appreciate that many variationsare possible in the exemplary embodiments without materially departingfrom the novel teachings and advantages of the present disclosure.Accordingly, all such variations are intended to be included within thescope of the present disclosure.

The herein disclosed subject matter is to be considered descriptive andillustrative only, and the appended Claims are of a scope intended tocover and encompass not only the particular embodiment(s) disclosed, butalso equivalent structures, methods, and/or uses.

INDUSTRIAL APPLICABILITY

An ultrasonic image generating device and an image generating methodaccording to one or more exemplary embodiments disclosed herein has highavailability particularly in medical diagnostic device industries.

1. An ultrasonic image generating device which generates a cross-sectional image of a specific cross-section of a subject from a plurality of ultrasonic images obtained by scanning the subject from a plurality of directions using an ultrasonic probe, the ultrasonic image generating device comprising: a cross-section position identifying unit configured to obtain cross-section information indicating a position and an orientation of the specific cross-section; a positional information obtaining unit configured to obtain positional information including a position and an orientation of each of the ultrasonic images of the subject; a reference image selecting unit configured to select at least one of the ultrasonic images as a reference image, the at least one of the ultrasonic images having a distance from the specific cross-section that is less than a first threshold and an orientation difference from the specific cross-section that is less than a second threshold; and a cross-sectional image generating unit configured generate the cross-sectional image using the reference image.
 2. The ultrasonic image generating device according to claim 1, wherein the specific cross-section includes a region of interest, and the reference image selecting unit is configured to select, as the reference image, an ultrasonic image having a distance from a point included in the region of interest in the specific cross-section that is less than the first threshold and an orientation difference from the specific cross-section that is less than the second threshold.
 3. The ultrasonic image generating device according to claim 1, wherein the reference image selecting unit is configured to select an ultrasonic image as the reference image from the ultrasonic images, for each of a plurality of regions obtained by dividing the specific cross-section, the ultrasonic image having a distance from the region that is less than the first threshold and an orientation difference from the specific cross-section that is less than the second threshold, and the cross-sectional image generating unit is configured to generate an image of each of the regions using the reference image selected for the region.
 4. The ultrasonic image generating device according to claim 3, wherein the reference image selecting unit is configured to select an ultrasonic image as the reference image from the ultrasonic images for each of the regions, the ultrasonic image having a distance from a central point of the region that is less than the first threshold and an orientation difference from the specific cross-section that is less than the second threshold.
 5. The ultrasonic image generating device according to claim 1, wherein the positional information obtaining unit is configured to obtain a position and an orientation of the ultrasonic probe to calculate the positional information based on the position and the orientation of the ultrasonic probe.
 6. The ultrasonic image generating device according to claim 5, wherein the positional information obtaining unit is further configured to obtain a direction of ultrasonic waves emitted from the ultrasonic probe to calculate the positional information based on the direction of the ultrasonic waves and the position and the orientation of the ultrasonic probe.
 7. The ultrasonic image generating device according to claim 1, wherein the first threshold is less than or equal to a resolution in a C—plane that is parallel to a scanning direction of the ultrasonic probe, and the second threshold is less than or equal to 30 degrees.
 8. The ultrasonic image generating device according to claim 1, wherein, when the ultrasonic images do not include the ultrasonic image having a distance from the specific cross-section that is less than the first threshold and an orientation difference from the specific cross-section that is less than the second threshold, the cross-sectional image generating unit is configured to generate the cross-sectional image using an ultrasonic image which is included in the ultrasonic images and has a smallest distance from the specific cross-section.
 9. The ultrasonic image generating device according to claim 1, further comprising a volume generating unit configured to generate a volume image from the ultrasonic images, wherein the cross-section position identifying unit is configured to generate the cross-section information indicating the specific cross-section identified by a user with respect to the volume image.
 10. The ultrasonic image generating device according to claim 1, wherein the reference image selecting unit is configured to (i) select, as the reference image, an ultrasonic image having a distance from the specific cross-section that is less than the first threshold and an orientation difference from the specific cross-section that is less than the second threshold, when the specific cross-section includes a region of interest, and (ii) select the reference image based only on the distance from the specific cross-section out of the distance from the specific cross-section and the orientation difference from the specific cross-section, when the specific cross-section does not include the region of interest.
 11. The ultrasonic image generating device according to claim 1, wherein the reference image including a plurality of reference images, and the crass-sectional image generating unit is configured to (i) generate a pixel value of a pixel included in the cross-sectional image by multiplying a pixel value of a pixel included in each of the reference images by a weighting coefficient and summing resulting pixel values, and (ii) increase the weighting coefficient for a reference image having a smaller orientation difference from the specific cross-section among the reference images.
 12. The ultrasonic image generating device according to claim 11, wherein the cross-sectional image generating unit is configured to increase the weighting coefficient for a reference image having a smaller orientation difference from the specific cross-section, the reference image being included in the reference images and having a distance from the specific cross-section that is less than a third threshold.
 13. An ultrasonic image generating device which generates a cross-sectional image from a plurality of Doppler images each of which indicates blood flow, the cross-sectional image indicating blood flow in a specific cross-section of a subject, the Doppler images being obtained by scanning the subject from a plurality of directions using an ultrasonic probe, the ultrasonic image generating device comprising: a cross-section position identifying unit configured to obtain cross-section information indicating a position and an orientation of the specific cross-section; a blood flow direction obtaining unit configured to obtain blood flow information indicating a direction of the blood flow in the specific cross-section; a positional information obtaining unit configured to obtain positional information including a position and an orientation of each of the Doppler images of the subject; a reference image selecting unit configured to select at least one of the Doppler images as a reference image, the at least one of the Doppler images having a distance from the specific cross-section that is less than a first threshold and an orientation different from the direction of the blood flow by less than a second threshold; and a cross-sectional image generating unit configured generate the cross-sectional image using the reference image.
 14. A method for generating a cross-sectional image of a specific cross-section of a subject from a plurality of ultrasonic images obtained by scanning the subject from a plurality of directions using an ultrasonic probe, the method comprising: obtaining cross-section information indicating a position and an orientation of the specific cross-section; obtaining positional information including a position and an orientation of each of the ultrasonic images of the subject; selecting at least one of the ultrasonic images as a reference image, the at least one of the ultrasonic images having a distance from the specific cross-section that is less than a first threshold and an orientation difference from the specific cross-section that is less than a second threshold; and generating the cross-sectional image using the reference image.
 15. A method for generating a cross-sectional image from a plurality of Doppler images each of which indicates blood flow, the cross-sectional image indicating blood flow in a specific cross-section of a subject, the Doppler images being obtained by scanning the subject from a plurality of directions using an ultrasonic probe, the method comprising: obtaining cross-section information indicating a position and an orientation of the specific cross-section; obtaining blood flow information indicating a position and an orientation of each of the Doppler images of the subject, obtaining positional information including a position and an orientation of each of the Doppler images of the subject selecting at least one of the Doppler images as a reference image, the at least one of the Doppler images having a distance from the specific cross-section that is less than a first threshold and an orientation different from the direction of the blood flow by less than a second threshold; and generating the cross-sectional image using the reference image. 